A text value that is consistent with the item's type may be required. For example, if you are creating or updating a message, the IPM.Note or another class that is consistent with a message is required. An empty value is not allowed. But if you are creating or updating an item, an empty type is valid.

An error is returned if the ItemClass is set to a value that is inconsistent with the item type. For example, a message's ItemClass cannot be set to the ItemClass value for a Task.